patch 9.0.0869: bogus error when string used after :elseif

Problem:    Bogus error when string used after :elseif.
Solution:   Do not consider a double quote the start of a comment.
            (closes #11534)
diff --git a/src/testdir/test_vimscript.vim b/src/testdir/test_vimscript.vim
index 4aa6bca..a23bac3 100644
--- a/src/testdir/test_vimscript.vim
+++ b/src/testdir/test_vimscript.vim
@@ -192,6 +192,16 @@
     call assert_equal('ab3j3b2c2b1f1h1km', g:Xpath)
 endfunc
 
+" Check double quote after skipped "elseif" does not give error E15
+func Test_skipped_elseif()
+  if "foo" ==? "foo"
+      let result = "first"
+  elseif "foo" ==? "foo"
+      let result = "second"
+  endif
+  call assert_equal('first', result)
+endfunc
+
 "-------------------------------------------------------------------------------
 " Test 4:   :return							    {{{1
 "-------------------------------------------------------------------------------